Skin wound trauma, following high-dose radiation exposure, amplifies and prolongs skeletal tissue loss.

The present study investigated the detrimental effects of non-lethal, high-dose (whole body) γ-irradiation on bone, and the impact that radiation combined with skin trauma (i.e. combined injury) has on long-term skeletal tissue health. Recovery of bone after an acute dose of radiation (RI; 8 Gy), skin wounding (15-20% of total body skin surface), or combined injury (RI+Wound; CI) was determined 3, 7, 30, and 120 days post-irradiation in female B6D2F1 mice and compared to non-irradiated mice (SHAM) at each time-point. CI mice demonstrated long-term (day 120) elevations in serum TRAP 5b (osteoclast number) and sclerostin (bone formation inhibitor), and suppression of osteocalcin levels through 30 days as compared to SHAM (p<0.05). Radiation-induced reductions in distal femur trabecular bone volume fraction and trabecular number through 120 days post-exposure were significantly greater than non-irradiated mice (p<0.05) and were exacerbated in CI mice by day 30 (p<0.05). Negative alterations in trabecular bone microarchitecture were coupled with extended reductions in cancellous bone formation rate in both RI and CI mice as compared to Sham (p<0.05). Increased osteoclast surface in CI animals was observed for 3 days after irradiation and remained elevated through 120 days (p<0.01). These results demonstrate a long-term, exacerbated response of bone to radiation when coupled with non-lethal wound trauma. Changes in cancellous bone after combined trauma were derived from extended reductions in osteoblast-driven bone formation and increases in osteoclast activity.

Increased Osseous (99m)Tc-DPD Uptake in End-Stage Ankle Osteoarthritis: Correlation Between SPECT-CT Imaging and Histologic Findings.

BACKGROUND: We analyzed the histopathologic findings in end-stage osteoarthritic ankle joint tissue that display increased uptake of bone-seeking radiotracer in single-photon emission computed tomography-computed tomography (SPECT-CT) imaging. METHODS: Six consecutive patients with end-stage osteoarthritis undergoing total ankle replacement received preoperative SPECT-CT imaging using (99m)Technetium dicarboxypropane diphosphonate ((99m)Tc-DPD). Using imaging data for stratification, osteochondral tissue sections were prepared from SPECT-positive (+) and -negative (-) areas of tibial and talar resection specimens. Histomorphometric analyses of osteoblast numbers, collagen deposition, and cartilage degeneration were performed on hematoxylin and eosin, van Gieson's and Safranin-O stained tissue sections. Osteoclast activity was visualized using tartrate-resistant acid phosphatase (TRAP) staining. RESULTS: Increased (99m)Tc-DPD uptake was observed exclusively subjacent to the subchondral bone plate of tibial and talar joint compartments. SPECT(-) tissues displayed typical fatty marrow morphology containing mainly collagen-positive blood vessels and few marrow and bone-lining cells. SPECT(+) tissues were characterized by increased numbers of active bone-lining osteoblasts depositing collagen fibers. Collagen area fraction of subchondral bone marrow was significantly increased in SPECT(+) (0.52 ± 0.21) compared with SPECT(-) (0.29 ± 0.13) tissues (P = .30). Multinucleated TRAP(+) osteoclasts were absent from bone formation sites, but associated with vascular structures invading articular cartilage through the subchondral bone plate. Increased (99m)Tc-DPD uptake was specifically and strongly correlated with increased osteoblast numbers (P = .011), and with collagen area fraction (P = .030) but not with Mankin score (P = .202), or with osteoclast number (P = .576). CONCLUSION: Subchondral bone tissues in SPECT(+) areas of end-stage ankle osteoarthritis were histologically characterized by increased osteoblast-mediated bone formation in the absence of functional osteoclasts, and increased cellularity and collagen deposition in marrow tissues. CLINICAL SIGNIFICANCE: Our findings suggest a pathologic bone-remodeling process in end-stage ankle OA areas with increased (99m)Tc-DPD uptake.

Progranulin plays crucial roles in preserving bone mass by inhibiting TNF-α-induced osteoclastogenesis and promoting osteoblastic differentiation in mice.

A close correlation between atherosclerosis, inflammation, and osteoporosis has been recognized, although the precise mechanism remains unclear. The growth factor progranulin (PGRN) is expressed in various cells such as macrophages, leukocytes, and chondrocytes. PGRN plays critical roles in a variety of diseases, such as atherosclerosis and arthritis by inhibiting Tumor Necrosis Factor-α (TNF-α) signaling. The purpose of this study was to investigate the effect of PGRN on bone metabolism. Forty-eight-week old female homozygous PGRN knockout mice (PGRN-KO) (n = 8) demonstrated severe low bone mass in the distal femur compared to age- and sex-matched wild type C57BL/6J mice (WT) (n = 8) [BV/TV (%): 5.8 vs. 16.6; p < 0.001, trabecular number (1/mm): 1.6 vs. 3.8; p < 0.001]. In vitro, PGRN inhibited TNF-α-induced osteoclastogenesis from spleen cells of PGRN-KO mice. Moreover, PGRN significantly promoted ALP activity, osteoblast-related mRNA (ALP, osteocalcin) expression in a dose-dependent manner and up-regulated osteoblastic differentiation by down-regulating phosphorylation of ERK1/2 in mouse calvarial cells. In conclusion, PGRN may be a promising treatment target for both atherosclerosis and inflammation-related osteoporosis.

Single-photon-emission computed tomography in painful total ankle replacements.

BACKGROUND: The use of single-photon-emission computed tomography (SPECT) in identifying unexplained pain in the foot and ankle has been described, where other imaging modalities have failed. The investigation of a painful total ankle replacement (TAR) is difficult, often not delineating a definitive cause. Our aim in this study was to investigate the use of SPECT-CT imaging in painful TARs. METHODS: We performed a retrospective analysis of SPECT imaging performed for painful TARs in our department between October 2010 and December 2014. There were 14 patients identified who had undergone SPECT-CT imaging for a painful TAR. The mean age was 63.1 years, with a male/female sex ratio of 2:3 and a minimum time from surgery to imaging of 18 months. RESULTS: Of the 14 patients, 13 were positive for increased osteoblastic activity in relation to the periprosthetic area consistent with implant loosening. The most common finding was tracer activity in relation to the talar component in 13 cases. There was additional tracer activity localized to the tibial component in 5 of these cases. In 10 of the 13 cases with prosthetic loosening/failure of bony ongrowth, there was no evidence of loosening on the plain radiographs. Infection was ruled out by using joint aspiration as clinically indicated. CONCLUSION: In our series, SPECT-CT imaging revealed a high incidence of medial sided talar prosthesis activity consistent with loosening. The finding of a high incidence of talar nonintegration illustrates the limitations of conventional radiology in follow-up of total ankle replacements, as this was not apparent on plain radiographs. We therefore conclude that there should be a high index of suspicion for talar prosthesis nonintegration in patients with otherwise unexplained ongoing medial pain in total ankle replacements. LEVEL OF EVIDENCE: Level IV, retrospective case series.

Load regulates bone formation and Sclerostin expression through a TGFß-dependent mechanism.

Bone continually adapts to meet changing physical and biological demands. Osteoblasts, osteoclasts, and osteocytes cooperate to integrate these physical and biochemical cues to maintain bone homeostasis. Although TGFß acts on all three of these cell types to maintain bone homeostasis, the extent to which it participates in the adaptation of bone to mechanical load is unknown. Here, we investigated the role of the TGFß pathway in load-induced bone formation and the regulation of Sclerostin, a mechanosensitive antagonist of bone anabolism. We found that mechanical load rapidly represses the net activity of the TGFß pathway in osteocytes, resulting in reduced phosphorylation and activity of key downstream effectors, Smad2 and Smad3. Loss of TGFß sensitivity compromises the anabolic response of bone to mechanical load, demonstrating that the mechanosensitive regulation of TGFß signaling is essential for load-induced bone formation. Furthermore, sensitivity to TGFß is required for the mechanosensitive regulation of Sclerostin, which is induced by TGFß in a Smad3-dependent manner. Together, our results show that physical cues maintain bone homeostasis through the TGFß pathway to regulate Sclerostin expression and the deposition of new bone.

Multimodal µCT/µMR based semiautomated segmentation of rat vertebrae affected by mixed osteolytic/osteoblastic metastases.

PURPOSE: Multimodal microimaging in preclinical models is used to examine the effect of spinal metastases on bony structure; however, the evaluation of tumor burden and its effect on microstructure has thus far been mainly qualitative or semiquantitative. Quantitative analysis of multimodality imaging is a time consuming task, motivating automated methods. As such, this study aimed to develop a low complexity semiautomated multimodal µCT/µMR based approach to segment rat vertebral structure affected by mixed osteolytic/osteoblastic destruction. METHODS: Mixed vertebral metastases were developed via intracardiac injection of Ace-1 canine prostate cancer cells in three 4-week-old rnu/rnu rats. µCT imaging (for high resolution bone visualization), T1-weighted µMR imaging (for bone registration), and T2-weighted µMR imaging (for osteolytic tumor visualization) were conducted on one L1, three L2, and one L3 vertebrae (excised). One sample (L1-L3) was processed for undecalcified histology and stained with Goldner's trichome. The µCT and µMR images were registered using a 3D rigid registration algorithm with a mutual information metric. The vertebral microarchitecture was segmented from the µCT images using atlas-based demons deformable registration, levelset curvature evolution, and intensity-based thresholding techniques. The µCT based segmentation contours of the whole vertebrae were used to mask the T2-weighted µMR images, from which the osteolytic tumor tissue was segmented (intensity-based thresholding). RESULTS: Accurate registration of µCT and µMRI modalities yielded precise segmentation of whole vertebrae, trabecular centrums, individual trabeculae, and osteolytic tumor tissue. While the algorithm identified the osteoblastic tumor attached to the vertebral pereosteal surfaces, it was limited in segmenting osteoblastic tissue located within the trabecular centrums. CONCLUSIONS: This semiautomated segmentation method yielded accurate registration of µCT and µMRI modalities with application to the development of mathematical models analyzing the mechanical stability of metastatically involved vertebrae and in preclinical applications evaluating new and existing treatment effects on tumor burden and skeletal microstructure.

Follow-up CT and MR findings of osteoblastic spinal metastatic lesions after stereotactic radiotherapy.

PURPOSE: We retrospectively analyzed pre and post-stereotactic radiotherapy CT and MRI findings and volume changes for osteoblastic spinal metastatic lesions. MATERIALS AND METHODS: Of 114 lesions in 72 patients, 11 were osteoblastic. CT and MR images were reviewed to determine tumor volume, CT attenuation, T2 signal intensities, and contrast enhancement. RESULTS: Tumor volume did not change for 10 lesions and increased for 1 lesion. CT attenuation increased for 8 lesions with heterogeneous T2 signal intensities. Of these 8 lesions, 4 had patterns of dark signal foci and the other 4 had patterns of both dark and bright signal foci. T2 signal intensity became heterogenous, with dark and bright foci, for 2 of 3 lesions for which CT attenuation decreased, and normalized for the third lesion. The degree of contrast enhancement decreased for 6 lesions and did not change for 5 lesions. CONCLUSION: There were no changes in volume except for one case. On CT images, sclerotic changes were more common than loss of sclerotic foci. On T2-weighted images, dark signal intensities with or without bright signal foci developed and the degree of enhancement decreased for more than half of the cases.

The CT flare response of metastatic bone disease in prostate cancer.

BACKGROUND: New or worsening bone lesions in patients responding to treatment, known as the flare phenomenon is well described on (99m)Tc-MDP bone scintigraphy, but to our knowledge has not previously been described on CT. The appearance of new or worsening bone sclerosis on CT in patients with prostate cancer may therefore be erroneously classified as disease progression. PURPOSE: To assess the incidence of osteoblastic healing flare response at 3-month CT assessment in patients with castrate-resistant prostate cancer and to identify associated features that enable differentiation from progressive metastatic bone disease at 3 months. MATERIAL AND METHODS: CT scans of 67 patients with castrate-resistant prostate cancer undergoing treatment were reviewed by a radiologist blinded to clinical outcome. Changes in number, size, and density of metastatic bone lesions were documented and Response Evaluation Criteria in Solid Tumours (RECIST) in soft tissue lesions, alkaline phosphatase, prostate specific antigen, and (99m)Tc-MDP bone scans were used for correlation. RESULTS: Of the 39 patients who had 3- and 6-month follow-up, eight patients (21%) demonstrated an increase in number, size, or density of sclerotic lesions on the 3-month CT scan despite improvement in PSA and soft tissue lesions. Three out of eight patients (8%) maintained partial response/remained stable at follow-up and were defined as showing a flare response: in this group bone metastases evident on CT showed a qualitative and quantitative increase in density and no lesions faded at 3 months. In contrast, in all patients who progressed at 3 months by PSA/RECIST criteria (n = 8) bone lesions showed a mixed pattern with some lesions increasing and others decreasing in density. CONCLUSION: The incidence of flare response of metastatic bone disease evident at 3-month post-treatment CT in patients with prostate cancer undergoing systemic treatment is 8%. In patients with falling PSA and stable/responding soft tissue disease at 3 months an increase in bone sclerosis in the absence of fading bone metastases can be interpreted as flare and is likely to represent a response.

Percutaneous vertebroplasty as a treatment for painful osteoblastic metastatic spinal lesions.

Percutaneous vertebroplasty (PVP) has been used widely to treat pain caused by osteolytic spinal lesions, whereas vertebroplasty for osteoblastic spinal lesions is less known. The purpose of this study is to describe PVP as a highly effective miniinvasive procedure to treat painful osteoblastic metastatic spinal lesions. Four patients with painful osteoblastic metastatic spinal lesions were treated by PVP in the authors' department, and immediately relief of pain was achieved in all of them. The findings from this study may encourage more studies of PVP in palliative treatment of patients with osteoblastic lesions.

Osteoblastoma.

Osteoblastoma is a rare benign bone tumor. Although the histologic features in most cases are distinctive, there are various permutations that make the diagnosis challenging. It can mimic a variety of other benign bone tumors, but more importantly, distinguishing it from osteoblastoma-like osteosarcoma can be difficult. In this case report, I describe the clinicopathologic findings for a 13-year-old adolescent boy with T7 spinal osteoblastoma and review salient clinical, radiographic, and pathologic features of osteoblastoma, as well as the differential diagnoses.

Scintigraphic evaluation of osteoblastic activity in extraction sockets treated with platelet-rich fibrin.

PURPOSE: To evaluate the effect of platelet-rich fibrin (PRF) on the early bone healing process with bone scintigraphy based on technetium-99m methylene diphosphonate uptake in third molar extraction sockets. PATIENTS AND METHODS: Fourteen patients with bilaterally soft tissue impacted third mandibular molars were included in the study. The right and left impacted third molars were surgically extracted in the same session. PRF was randomly administered into one of the extraction sockets, whereas the contralateral sockets were left without treatment. Four weeks after surgery, scintigrams were obtained to evaluate scintigraphic differences between PRF-treated and non-PRF-treated sockets. After completion of the clinical study, PRF samples were evaluated by light and scanning electron microscopy. RESULTS: The average increase in technetium-99m methylene diphosphonate uptake as an indication of enhanced bone healing did not differ significantly between PRF-treated and non-PRF-treated sockets 4 weeks postoperatively (P > .05). Abundant fibrin and inflammatory cells were observed by light microscopic examination of PRF samples. Scanning electron microscopic analysis of PRF revealed the existence of platelet aggregates in a fibrin network and crystalline particles on the outer surface of PRF. CONCLUSIONS: PRF might not lead to enhanced bone healing in soft tissue impacted mandibular third molar extraction sockets 4 weeks after surgery. PRF exhibits the potential characteristics of an autologous fibrin matrix. However, whether the presence of crystal-like particles on the outer surface of PRF alters bone healing should be investigated further.

Progressive osteoblastic bone metastases in breast cancer negative on FDG-PET.

Positron emission tomography using F-18 fluorodeoxyglucose positron emission tomography (FDG-PET) is increasingly used in breast cancer. The new generation cameras integrate PET and CT within the same camera, allowing the simultaneous assessment of the structural and metabolic aspects of disease. There is presently a controversy on the clinical significance of osteoblastic bone metastases in breast cancer which are not detected on FDG-PET. It has been suggested that these radiologically dense lesions represent the result of successful treatment of initially osteolytic lesions. We report a case of a 65-year-old woman with a suspicion of recurrent breast cancer based on an increasing serum tumor marker. Serial PET/CT showed progressive blastic bone metastases on the CT without FDG uptake. These lesions were confirmed by bone single photon emission computed tomography. This case report shows: first, that progressive osteoblastic lesions can lack FDG-avidity, leading to a false-negative PET; and secondly, that bone scintigraphy should not be replaced by FDG-PET/CT for the detection of bone metastases in breast cancer.

Osteoblastic and osteolytic human osteosarcomas can be studied with a new xenograft mouse model producing spontaneous metastases.

There is no animal model that reflects the histological and radiographical heterogeneity of osteosarcoma. We assessed seven osteosarcoma cell lines for their potential to develop orthotopic tumors and lung metastasis in SCID mice. Whereas radiologically, 143B developed osteolytic tumors, SaOS-LM7 developed osteoblastic primary tumors. The mineralization status was confirmed by assessing the alkaline phosphatase activity and the microarray expression profile. We herein report a xenograft orthotopic osteosarcoma mouse model to assess osteoblastic and osteolytic lesions, which may contribute in the search for new diagnostic and therapeutic approaches.

Osteoblastic response as a healing reaction to chemotherapy mimicking progressive disease in patients with small cell lung cancer.

The osteoblastic response (OR) phenomenon as a healing reaction during effective chemotherapy-defined by the appearance of new osteoblastic bone lesions while disease response in other tumor sites was well documented-has previously been described for breast and prostate cancer. The purpose of this study was to investigate this phenomenon that could erroneously be interpreted as progressive disease in patients with small cell lung cancer (SCLC) and to establish guidelines for interpretation of follow-up computed tomography (CT) examinations in this situation. Twenty-four patients with newly diagnosed SCLC and bone metastases were retrospectively included in this study. The characteristics of bone lesions in CT examinations were correlated with bone scintigraphy and magnetic resonance imaging, if available. In target lesions the CT density quantified in Hounsfield units (HU) was evaluated at baseline and during follow-up. New osteoblastic lesions occurred during follow-up in 17 of 24 patients. OR was proven in 4 patients and considered most likely in 11 patients; mean density increase in target lesions was 153 HU. The study indicates that osteoblastic response as a healing reaction seems to occur in the majority of patients with SCLC and bone metastases and should not be misinterpreted as progressive disease.

Development of a low-dose anti-resorptive drug regimen reveals synergistic suppression of bone formation when coupled with disuse.

Safe and effective countermeasures to spaceflight-induced osteoporosis are required to mitigate the potential for mission-critical fractures and ensure long-term bone health in astronauts. Two anti-resorptive drugs, the bisphosphonate zoledronic acid (ZOL) and the anti-receptor activator of NF-kappaB ligand protein osteoprotegerin (OPG), were investigated to find the minimum, comparable doses that yield a maximal increase in bone quality, while minimizing deleterious effects on turnover and mineralization. Through a series of five trials in normally loaded female mice (n = 56/trial), analysis of trabecular volume fraction and connectivity using microcomputed tomography, along with biomechanical testing, quantitative histomorphometry, and compositional analysis, was used to select 45 microg/kg ZOL and 500 microg/kg OPG as doses that satisfy these criteria. These doses were then examined for their ability to mitigate bone loss following short-term unloading through hindlimb suspension (HLS). Seventy-two mice were prophylactically administered ZOL, OPG, or PBS and assigned to loaded control or 2-wk HLS groups (n = 12 for each of 6 groups). Both anti-resorptives were able to preserve trabecular microarchitecture and femoral elastic and maximum force in HLS mice (+30-40% ZOL/OPG vs. PBS). In HLS mice, anti-resorptive dosing reduced resorption perimeter at the femoral endocortical surface by 30% vs. PBS. In loaded control mice, anti-resorptives produced no change in bone formation rate; however, reductions in bone formation rate brought about by HLS were exacerbated by anti-resorptive treatment, suggesting synergistic inhibition of osteoblasts during disuse. Refined anti-resorptive dosing will tend to target countermeasures to the period of disuse, resulting in faster recovery and less adverse effects for astronauts.

Kinetics of in vivo bone deposition by bone marrow stromal cells within a resorbable porous calcium phosphate scaffold: an X-ray computed microtomography study.

Resorbable ceramic scaffolds based on Silicon stabilized tricalcium phosphate (Si-TCP) were seeded with bone marrow stromal cells (BMSC) and ectopically implanted for 2, 4, and 6 months in immunodeficient mice. Qualitative and quantitative evaluation of the scaffold material was performed by X-ray synchrotron radiation computed microtomography (microCT) with a spatial resolution lower than 5 microm. Unique to these experiments was that microCT data were first collected on the scaffolds before implantation and then on the same scaffolds after they were seeded with BMSC, implanted in the mice and rescued after different times. Volume fraction, mean thickness and thickness distribution were evaluated for both new bone and scaffold phases as a function of the implantation time. New bone thickness increased from week 8 to week 16. Data for the implanted scaffolds were compared with those derived from the analysis of the same scaffolds prior to implantation and with data derived from 100% hydroxyapatite (HA) scaffold treated and analyzed in the same way. At variance with findings with the 100% HA scaffolds a significant variation in the density of the different Si-TCP scaffold regions in the pre- and post-implantation samples was observed. In particular a post-implantation decrease in the density of the scaffolds, together with major changes in the scaffold phase composition, was noticeable in areas adjacent to newly formed bone. Histology confirmed a better integration between new bone and scaffold in the Si-TCP composites in comparison to 100% HA composites where new bone and scaffold phases remained well distinct.